[PATCH] Sema: Fix some undefined behaviour when acting on redeclarations

[Justin Bogner]

If we hit an error already, we may have set Name to nullptr, which
means calling isAcceptableTagRedeclaration hits UB. Avoid this like we
do elsewhere in the function by checking Name first.

We could also fix this by passing OrigName instead, since the name is
only used for diagnostics anyway. Should I do that instead, or is this
good to commit?


commit 203946970eafb48a120b29dfac1612b8762b9115
Author: Justin Bogner <m...@justinbogner.com>
Date:   Mon Jun 22 00:05:05 2015 -0700

    Sema: Fix some undefined behaviour when acting on redeclarations
    
    If we hit an error already, we may have set Name to nullptr, which
    means calling isAcceptableTagRedeclaration hits UB. Avoid this like we
    do elsewhere in the function by checking Name first.

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index ce89d99..8c94460 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -11747,9 +11747,9 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                         SS.isNotEmpty() || isExplicitSpecialization)) {
         // Make sure that this wasn't declared as an enum and now used as a
         // struct or something similar.
-        if (!isAcceptableTagRedeclaration(PrevTagDecl, Kind,
-                                          TUK == TUK_Definition, KWLoc,
-                                          *Name)) {
+        if (Name && !isAcceptableTagRedeclaration(PrevTagDecl, Kind,
+                                                  TUK == TUK_Definition, KWLoc,
+                                                  *Name)) {
           bool SafeToContinue
             = (PrevTagDecl->getTagKind() != TTK_Enum &&
                Kind != TTK_Enum);

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